1. Field of the Invention
This invention generally relates to liquid crystal display (LCD) and integrated circuit (IC) fabrication, and more particularly, to a high-quality isotropic polycrystalline silicon (poly-Si) film and a corresponding laser irradiation fabrication process.
2. Description of the Related Art
When forming thin film transistors (TFTs) for use in LCD or other microelectronic circuits, the location of transistor channel regions, the orientation of regular structured poly-Si or single-grain-crystalline silicon, grain boundaries, and surface roughness are important issues. Such poly-Si material can be used as the active layer of poly-Si TFTs in the fabrication of active-matrix (AM) backplanes. These backplanes, in turn, can be used in the fabrication of AM LCDs and can be also combined with other display technologies, such as organic light-emitting diodes (OLEDs).
Poly-Si material is typically formed by the crystallization of an initially deposited amorphous Si (a-Si) films. This process can be accomplished via solid-phase-crystallization (SPC), i.e., by annealing a-Si films in a furnace at an appropriate temperature, for a sufficiently long time. Alternatively, laser annealing can also be used to achieve the phase transformation.
Conventionally, all crystallization techniques are applied to a given substrate in such a manner as to yield poly-Si film of a uniform quality throughout the substrate area. In other words, there is no spatial quality differentiation over the area of the substrate. For example, when a-Si film is annealed in a furnace or by rapid-thermal-annealing, the entire layer is exposed to the same temperature, resulting in the same quality of poly-Si material. In the case of conventional laser annealing, some differentiation is possible, but the price, in terms of loss of throughput, is very high for the modest performance gains. Hence, even for conventional laser annealing, quality differentiation is not practically feasible.
It would be advantageous if a high throughput laser annealing process could produce high quality, isotropic polycrystalline silicon.
It would be advantageous if a high throughput laser annealing process could produce poly-Si with a higher percentage of lower-angle grain boundaries.